An Investigation Into Ball Grid Array Inspection Techniques

Gesa STM-261
Figure I. Simplified diagram of real-time
perpendicular transmission X-ray system.
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The programme of work presented in this report was devised to assess the detection
capabilities of four different commercially available X-ray inspection systems. In this
preliminary study common soldering defects were introduced during the assembly stage
of BGA packages. A simple double-sided PCB substrate was used to check for the most
common defects encountered during assembly by vapour phase methods. Most
spacecraft circuits now employ multilayer PCBs of between 8 and 28 layers together
with severa] ground planes of copper onto which component packages may be attached
to both sides of the board. Such complex boards will also be expected to support BGA
packages; they are expected to be far more difficult to inspect for soldering defects and
will be the subject of a follow-on study.
X-ray inspection is achieved by placing the workpiece to be inspected between an X-ray
source and an X-ray camera as shown in Figure]. The radiation emitted by the source is
absorbed and scattered as it passes through the workpiece. The camera collects the
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